Polytetrafluoroethylene (PTFE) is commercially known as Teflon which is one of the very useful thermostable and robust polymers. PTFE has several applications in various fields because it can sustain harsh environmental conditions. Typical applications of PTFE are known e.g. in corrosion resistant materials, cooking utensils, waterproof fabric, etc. Nevertheless, the use of polytetrafluoroethylene (PTFE) is restricted in various applications due to its chemical inertness and hydrophobic nature. For example, native porous PTFE is not suitable for water filtration membrane or leads to adhesion difficulties when used with other substrates such as metals, polymers and ceramic materials. Making PTFE hydrophilic would render PTFE more easily applicable.
For example, hydrophilic PTFE could be used as a water filtration membrane. Similarly, gluing or adhesion with other substrates could be improved, especially with other hydrophilic substrates. Consequently, hydrophilic PTFE will be suitable for attachment with other components (metal, polymers, and ceramic materials) for membrane support and other applications. In addition, after hydrophilic modification of PTFE, various functional coatings, such as for instance but not limited to metal coatings, can be deposited with ease which can lead to new directions of applications in the field of mechanics, optics, and electronics.
Some methods are known for achieving hydrophilic PTFE. In these known methods, hydrophilic PTFE is achieved by wet chemical methods which involve hazardous organic solvents, whereby long processing time is required to get rid of these solvents. Thus, these methods are time consuming and also involve chemical hazards. Other methods for obtaining hydrophilic PTFE are based on “growing” PTFE together with other hydrophilic polymer via copolymerization route.
It is known that one can obtain hydrophilic effects on polymers by plasma treatment, especially with oxygen plasma. Nevertheless, attempts to render native hydrophobic PTFE hydrophilic by applying oxygen plasma treatment did not succeed. Applying an oxygen plasma treatment renders PTFE more hydrophobic, as is for example described in Carbone et al. Surface Interface Anal. 2010 (42) 1014-1018 and Vandencasteele et al. Plasma Process. Polym. 2008 (5) 661.
In European Polymer Journal 44 (2008) p 3564-3570, Kemell et al. describe the use of thermal atomic layer deposition of Al2O3 and TiO2 thin films on polymeric substrates such as PTFE for modifying their surface. In order to check the hydrophobic behavior of PTFE the water contact angle is studied and it is reported that the water contact angle decreases upon performing atomic layer deposition (ALD), but only down to 99°. In the study of Kemell et al. increasing the number of cycles thereby does not seem to allow to further reduce the water contact angle. In order to further decrease the contact angle, and thus render PTFE more hydrophilic, UV illumination was applied. UV induced hydrophilic effect suffers from aging effect. The effect vanishes with time as experienced by Sakai et al. J. Phys Chem B 2003 (107) 1028-1035. Furthermore, it was shown in Kemell et al. that the deposited thin films on PTFE did not pass the Scotch tape test, indicating poor adhesion properties of the deposited films.
Consequently, there is still a need for a good and efficient method for rendering PTFE hydrophilic.